With the increase in a storage capacity of a storage apparatus, a technique for virtually allocating a physical resource such as a disk has received attention in recent years. In Thin Provisioning, the demanded amount of storage use is provided as a virtual volume by preparing only a physical disk capacity corresponding to the actual amount of storage use without preparing a physical disk capacity corresponding to the demanded amount of storage use. When the actual amount of storage use approaches a prepared physical disk capacity, only an additional physical disk capacity is added and operation is continuously performed. Thus, a Thin Provisioning volume is a variable allocation virtual volume to which a physical area (storage area) is variably allocated in accordance with a usage pattern. With such a Thin Provisioning volume, it is possible to establish a virtual volume having a capacity larger than the prepared physical disk capacity.
With the current progress of computerization, more data for the business continuity of a company or the like is stored in a storage apparatus. In this case, it is preferable to periodically back up data stored in a storage apparatus. Various backup mechanisms for effectively backing up data stored in a storage apparatus have been researched and developed. As one of these backup mechanisms, an advanced copy function of rapidly performing backup only with a storage apparatus without using the Central Processing Unit (CPU) of a server is known. Such an advanced copy function can be applied to a variable allocation virtual volume such as a Thin Provisioning volume.
Japanese Laid-open Patent Publications No. 2008-130080, No. 2008-181271, No. 2003-256148, and No. 02-093721 are examples of related art.
Examples of the above-described advanced copy function include a remote advanced copy function of typically backing up the volume of a copy source storage unit to the volume of a copy destination storage unit disposed far from the copy source storage unit. In the remote advanced copy function, when copying processing for copying data from a copy source to a copy destination starts, initial copying processing for sequentially transferring pieces of data in the copy range of the copy source to the copy destination in predetermined units is performed.
However, in a variable allocation virtual volume such as a Thin Provisioning volume, zero data is allocated to an area having no real data as dummy information. This means that zero is read from the area when data is read from the area by a server. Accordingly, when the area having no real data is subjected to copying in the above-described remote advanced copy function, as illustrated in FIG. 1, the zero data that is dummy information is remotely transferred from the area. As a result, a large amount of data is transferred. In FIG. 1, “allocated” represents a state in which a physical area (storage area) has already been allocated to a target virtual area (virtual block) in a virtual volume, and “unallocated” represents a state in which a physical area (storage area) is not allocated to a target virtual area (virtual block) in a virtual volume. Such transferring of unnecessary data becomes a serious problem when a remote line is a line with a low bandwidth.